The present invention relates generally to a method and apparatus for processing a data signal transferred using a specific data protocol.
In a data communication system, messages, in particular control messages, can be transmitted through a communication channel which can comprise at least one signal line. The signal line can be a physical wire or a data line of a data bus. For fault detection, measurement instruments such as oscilloscopes are used to decode and analyze a captured data signal.
Oscilloscopes allow observation of constantly varying input signals. Oscilloscopes are used to observe a change of an electrical signal over time displayed on a display unit of the oscilloscope. The observed waveform of the captured signal can be analyzed for signal properties such as amplitude, frequency, rise time, time interval, distortion. Conventional oscilloscopes can calculate these signal properties directly and display them to the user. A storage oscilloscope allows single events to be captured by the instrument which can be displayed on the display unit of the oscilloscope.
FIG. 1 shows a block diagram of a conventional digital oscilloscope. The illustrated digital oscilloscope comprises a preamplifier PA providing a variable amplification factor amplifying the input signal. After level matching, the preamplified analog measured signal can be supplied to an analog digital converter ADC for conversion into a corresponding digital data format. A digital oscilloscope further can comprise a unit COMP for compensation of delay times to compensate different delay times in the measurement channels associated with the individual measured signals. Further, an equalizer EQ can be provided which implements an equalization of the linear or respectively non-linear, distorted, digitized measured signals as shown in FIG. 1. Further, a digital triggering system TRIG can be provided. After equalization, the digitized measured signal is checked by the digital triggering system with reference to an adjustable triggering condition, and in the case of an identification of this triggering condition, the triggering signal for triggering the digital oscilloscope is generated in the measured signal at the output of the digital triggering system. Those sampled values of the digitized, equalized measured signal, which are registered simultaneously with the triggering signal or immediately following the triggering signal in time are displayed on a screen of a display unit DIS or recording unit of the respective digital oscilloscope as illustrated in FIG. 1.
Some conventional oscilloscopes provide a function to display a binary representation of the captured analog signal, for instance on a specific display area of the display unit of the oscilloscope. The captured data signals often represent a data bit stream transferred via a data bus line of a data bus from a data source such as a first processing unit to a data sink formed by another processing unit. These bit streams represent messages transferred via said data line according to a predetermined communication data protocol. The data protocol is a convention that can define the order and meaning of data bits in the digital data bit stream. Typically, a message comprises a predetermined data structure according to the used data protocol. The transported data signal can be damaged during transmission from a data source to a data sink so that one or several data bits are faulty. These faults data bits can cause that a decoding of the received data messages at the receiving data sink fails. A measurement apparatus such as an oscilloscope can be used to find the reason why and where a failure during data transmission has occurred. The decoding on the receiving side comprises normally a sequence of decoding steps which are performed in a decoding process. A conventional oscilloscope does not provide means to analyze each decoding process step of the decoding process separately in case that decoding fails.